Terephthalic acid di-esters, such as di-(2-ethylhexyl) terephthalate (also known as dioctyl terephthalate or DOTP), can be used as plasticizers in a variety of polymeric materials such as polyvinyl chloride.
DOTP is typically prepared by the titanate-catalyzed transesterification of dimethyl terephthalate (DMT) with 2-ethylhexanol (EH). This method, however, is not the most direct route to making DOTP. It requires the conversion of terephthalic acid (TPA) to DMT.
The most direct route to DOTP involves esterification of TPA with EH. Organo-titanates, such as tetraisopropoxy titanate, are among the best catalysts for this direct route. The reaction rate with these catalysts, however, is still significantly slower than the transesterification route.
Therefore, there is a need in the art for faster methods for forming DOTP directly from TPA.
The present invention addresses this need as well as others, which will become apparent from the following description and the appended claims.